Conductive Polymer-Semiconductor Junction: Characterization of Poly(3-methylthiophene):Cadmium Sulfide Based Photoelectrochemical and Photovoltaic Cells

The solid-state and electrochemical properties of the junction between highly doped metallic-like PMeT [PMeT=poly(3-methylthiophene)] and n-CdS are described. Electronic contact between the polymer and the semiconductor produces a Schottky barrier in the solid state. The rectification number, barrier height, quality factor, and photovoltaic response of the solid-state n-CdS:PMeT:Au cell compare favorably with those of n-CdS:metal Schottky barrier devices. When the solid-state device contacts various redox electrolytes, the junction characteristics are not altered appreciably as long as the polymer is doped to the metallically conductive state. Auger depth profile studies show that the PMeT film is relatively impermeable to redox species in solution. An energy-band model is invoked that accounts for both the independent behavior of the barrier height on the redox electrolyte and the impermeable nature of the film.